As is known, most currently used machines for metering liquid pharmaceutical products are what are known in the sector as "reciprocating machines", which substantially comprise a first body operating in steps and supporting a number of capsules in a spoke arrangement; a second body with internal channels and which rotates between two positions; a hopper full of liquid; and a number of hydraulic pistons. The second body, in a first position, connects the hopper hydraulically to the pistons into which a predetermined quantity of liquid is drawn, and, in a second position, connects the pistons hydraulically to respective capsules, which are arrested, for a predetermined time beneath the second body, pending injection of the liquid by the pistons into the capsules.
Machines of the above type have several drawbacks. In particular, as compared with continuously operating machines of the same overall size, reciprocating types provide for a much lower output rate per hour of capsules. What is more, at each operating step, reciprocating machines generate even severe vibration resulting not only in wear of the machine components but also in spillage of the liquid from the injected capsules, which in turn leads to other, no less serious, drawbacks, such as inaccurate filling of the capsules and fouling, or even stoppage, of the machine as a whole. Finally, on account of the cost and complications involved, reciprocating machines sometimes feature no devices for detecting the presence of capsules inside the respective seats, which, in the event of any missing capsules, results in further fouling and consequent stoppage of the machine.
To eliminate the above drawbacks of reciprocating machines, the present Applicant has devised a continuously operating machine as described in European Patent Application nr 91105443.5 filed on Apr. 5, 1991, and which comprises a rotary vessel full of liquid; a body having a number of hydraulic pistons; and a number of valves for channeling the liquid from the vessel to the pistons, and from the pistons to the capsules. The valves are slide types and are movable, along respective longitudinal axes, between a first position hydraulically connecting the vessel to the pistons, and a second position hydraulically connecting each piston to a corresponding capsule.
While undoubtedly affording advantages as compared with reciprocating machines, the above continuously operating machine also involves a number of drawbacks, especially at high speed. In particular, operation of the slide valves also results in vibration, which may even reach severe proportions at high speed, thus also resulting, albeit to a lesser degree than with reciprocating machines, in wear of the component parts of the machine, possible spillage, inaccurate filling of the capsules, and fouling of certain parts of the machine. Also, the seals on the slide valves are subject to rapid wear by the axial movement of the valves, thus resulting in all the drawbacks mentioned above relative to spillage on the outside of the machine.